Method, user equipment and application server for adding media stream of multimedia session

ABSTRACT

A method, user equipment and application server for adding media stream of multimedia session. A UE 1  establishes a multimedia session with a UE 2,  receives a media stream adding request directed at the multimedia session of the UE  1;  the media stream adding request includes an identity of a UE 3  and the media type of the media flow requested to be added; the UE 3  is controlled to establish a media stream of the media type with the UE 2.  Therefore, adding the media stream on the UE 3  is realized, and the user may realize the multimedia session with the peer end through multiple UEs, thereby avoiding the inconvenience that the media stream can only be added to the two parties in the session and living up to the users&#39; diversified requirements on the multimedia services.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2008/071216, filed on Jun. 6, 2008, which claims the benefitof Chinese Patent Application No. 200710146727.0, filed on Aug. 17,2007, both of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to the communication field, and inparticular to a method, user equipment and application server for addingmedia stream of multimedia session.

BACKGROUND OF THE INVENTION

Along with the development of the radio communication service, the usersare more and more demanding on the service quality and category, whichgives rise to many value-added services. These services bringconvenience to people's life and, at the same time, meet theirdiversified demands.

At present, in a multimedia session, two parties of the ongoing sessionare allowed to increase the media stream, for example, when aconversation goes on, the video phone becomes possible by adding thevideo media stream.

The existing method for adding the media stream of multimedia sessionincludes the following:

A first user equipment (UE1) establishes a multimedia session with asecond user equipment (UE2).

The UE1 sends a new media stream adding request to the UE2.

The UE2 accepts the adding request;

Between the UE1 and the UE2 transmits the added media stream.

It is understandable that the interacting of the messages between theUE1 and the UE2 needs to pass through the call control equipment.

During the research and implementation of the prior art, the inventorfinds the following drawbacks:

Although the above mentioned method of adding the media stream mayrealize adding a media stream during the multimedia session, the addingof the media stream is between the two parties of the session and athird user equipment (UE3) can not be added to receive and transmit theadded media stream. In the real situation, however, it is very likelythat one user owns more than one UE, each having its own strong points.For example, one user owns two UEs at the same time; one is good invoice quality, but does not support video or supports but with a pooreffect, while the other has powerful video function, but is poor invoice quality. If the existing method is adopted to add the mediastream, the respective strong points of the two UEs can not be broughtinto play. This limitation brings inconvenience to users of themultimedia service and makes it impossible to meet users' requirementson diversified multimedia service.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method, user equipmentand application server for adding media stream, which may realize addinga media stream on the third user equipment, UE3, so that the user mayenter into a multimedia session with the peer end.

An embodiment of the present invention provides a method for adding amedia stream of a multimedia session, including the following.

A UE1 establishes a multimedia session with a UE2 under the control ofan application server.

The UE1 sends to the application server a media stream adding requestdirected at the multimedia session, where the media stream addingrequest includes an identity of a UE3 and a media type of the mediastream requested to be added.

The UE3 establishes a media stream of the media type with the UE2 underthe control of the application server.

An embodiment of the present invention provides a method for adding themedia stream of the multimedia session, including the following.

A UE1 establishes a multimedia session with a UE2 under the control ofan application server.

A UE3 sends to the application sever a media stream adding request foradding the media stream with the UE2, where the media stream addingrequest includes a media type of the media stream to be added.

Media stream of the media type is established between the UE3 and theUE2 under the control of the application server.

An embodiment of the present invention provides a user equipment,including:

a session establishing unit, adapted to establish a session with the UE2under the control of the application server; and

a media adding request sending unit, adapted to send a media streamadding request directed at the multimedia session to the applicationserver, where the media adding request includes the identity of the UE3and the media type of the media stream requested to be added.

An embodiment of the present invention provides an application server,including:

a session control unit, adapted to control the UE1 to establish amultimedia session with the UE2;

a receiving unit, adapted to receive a media stream adding request ofthe UE1 which is directed at the multimedia session, where the mediastream adding request includes the ID of the UE3 and the media type ofthe media stream requested to be added; and

a media stream adding control unit, adapted to control the UE3 toestablish the media stream of the media type with the UE2.

An embodiment of the present invention provides a user equipment,including:

a media adding request sending unit, adapted to send the request foradding the media stream between the application server and the UE2;where the request includes the type of the added media stream; and

a media stream establishing unit, adapted to establish the added mediastream of the requested media type with the UE2 under the control of theapplication server.

An embodiment of the present invention provides an application server,including:

a session control unit, adapted to control the UE1 to establish amultimedia session with the UE2;

a receiving unit, adapted to receive a media stream adding request sentby the UE3 to add the media stream between the UE3 and the UE2, wherethe request includes the media type of the added media stream; and

a media stream adding unit, adapted to control the UE3 to establish amedia stream of the media type with the UE2.

In the embodiments of the present invention, the multimedia session isestablished between the UE1 and the UE2 under the control of theapplication sever; the UE1 sends to the application server a mediastream adding request directed at the multimedia session, where themedia stream adding request includes the identity of the UE3 and themedia type of the requested media stream; the UE3 establishes the mediastream of the media type with the UE2 under the control of theapplication server. Therefore, adding the media stream on the UE3 isrealized, and the user may realize the multimedia session with the peerend through multiple UEs, thereby avoiding the inconvenience that themedia stream can only be added to the two parties in the session andliving up to the users' diversified requirements on the multimediaservices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method for adding the media stream ofthe multimedia session in one embodiment of the present invention;

FIG. 2 is a flowchart showing that a multimedia session is establishedbetween a UE1 and the UE2 under the control of the application server inanother embodiment of the present invention;

FIG. 3 is a flowchart showing a method for adding the media stream ofthe multimedia session in one embodiment of the present invention;

FIG. 4 is a signaling flowchart of realizing the method embodiment byadopting the SIP protocol in one embodiment of the present invention;and

FIG. 5 is a signaling flowchart of realizing the method embodiment byadopting the SIP protocol in another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a method, user equipmentand application server for adding media stream of multimedia session,applicable in the technical field of communication. The following is adetailed description of the method, user equipment and applicationserver for adding media stream of multimedia session.

One embodiment of the present invention: A method for adding a mediastream of a multimedia session. As shown in FIG. 1, the method includesthe following:

Step a1: A UE1 establishes a multimedia session with a UE2 under thecontrol of an application server;

In this embodiment, the process for establishing multimedia sessionbetween the UE1 and the UE2 under the control of the application serveris in the following as illustrated in FIG. 2. The following exampletakes the UE2 as a call initiator.

Step b1: The UE2 sends to a Call Session Control Function, CSCF, asession Invite message for inviting the UE1 to join in the session;

Step b2: The CSCF performs a called initial Filter Criteria, iFC, check;after learning that the UE1 supports the media stream adding service,the CSCF sends the session Invite message to an application server;

Step b3: The application server sends the session Invite message to theUE1, where the session Invite message is forwarded to the UE1 via theCSCF;

Step b4: The UE1 sends a response message (200 OK) to the UE2, and thena multimedia session is established between the UE1 and the UE2.

It is understandable that, if the UE1 is the calling party, the processis basically the same as the above process with the followingdifference: if the Invite message for inviting the UE2 to join in thesession sent by the UE1 arrives at the CSCF, the CSCF performs thecalling iFC check; if it is learned that the UE1 supports the mediastream adding service, then the session Invite message is sent to theapplication server, and then the session Invite message is forwarded viathe CSCF to the UE2. The UE2 sends a response message (200 OK) to theUE1, and then a multimedia session is established between the UE1 andthe UE2.

That a session is established between the UE1 and the UE2 under thecontrol of the application server may also be realized in other ordinarymethods, which may not be a limitation to the present invention.

Step a2: The UE1 sends to the application server the media stream addingrequest directed at the multimedia session, where the media streamadding request includes the identity of the UE3 and the media type ofthe media stream requested to be added;

Step a3: The UE3 establishes the media stream of the media type underthe control of the application sever with the UE2.

In an embodiment of the present invention, the process of establishing amedia stream of the requested media type between the UE3 and the UE2 isas follows:

1. The application sever sends to the UE3 a session Invite message,where in the Session Invite, the address of the calling party may be theaddress of the application server or the identity of the UE2.

In an embodiment of the present invention, the identity of the UE may bean address, user name, nickname, etc of the UE; it is understandablethat as long as it can identify the UE, and help locating the UE, it maybe taken as the identity of the UE.

If the calling party in the multimedia session between the UE1 and theUE2 is the UE1, the address of the calling party is added into theidentity of the application server; if the calling party of themultimedia session is the UE2, and then, the address of the callingparty is added into identity of the UE2.

2. The UE3 and the UE2 perform the media information negotiationdirected at the media type under the control of the application server;the media negotiation is directed at the information of the media type,coding format that the two parties of the negotiation support, the portaddress of receiving and transmitting the media stream, etc. There maybe multiple information interactions during the negotiation which adoptsthe conventional technical means and the specific negotiating process isnot detailed here.

3. When the negotiation succeeds, the UE3 transmits the media stream ofthe media type to the UE2.

It is understandable that establishment of the media stream between theUE3 and the UE2 under the control of the application server may adoptother conventional procedure of which the establishing method does notlimit the present invention. In addition, the call connection betweenthe application server and the UE2 may be reused, which saves thereestablishment of a new call connection.

It is also understandable that in step a2, the media stream addingrequest sent by the UE1 to the application server may be triggered bythe UE1 under the operation of the user, or may be triggered when theUE1 receives the media adding request sent by the UE2, where the mediaadding request includes the media type of the added media stream.

In one embodiment of the present invention, a multimedia session isestablished between the UE1 and the UE2; the UE1 sends to theapplication server the media stream adding request directed at themultimedia session; the media stream adding request includes: theidentity of the UE3 or the media type of the media stream requested tobe added; the UE3 and the UE2 establish the media stream of the mediatype under the control of the application server. Since the media streamis added on the UE3, the user may enter into a multimedia session withthe peer end. As a result, it is avoided that the media stream can onlybe added on the two parties of the session, which brings inconvenienceto the user; therefore, the users' requirements on diversifiedmultimedia service are met.

Those skilled in the art may understand that all or part of the processin the above embodiments may be realized in the way of ordering therelated hardware by the program. The program may be stored in computerreadable storage medium; and when being executed, the program includesthe following steps:

The UE1 establishes multimedia session with the UE2 under the control ofthe application server;

The UE1 sends to the application server a media stream adding requestdirected at a multimedia session; the media stream adding requestincludes the identity of the UE3 and the media type of the requestedmedia stream;

The UE3 establishes with the UE2 the media stream of the media typeunder the control of the application server.

The above mentioned storage media may be read-only memory, disk orcompact disk.

One embodiment of the present invention

A media stream adding method of multimedia session, as shown in FIG. 3,includes the following steps:

Step c1: The UE1 establishes multimedia session with the UE2 under thecontrol of the application server.

For the specific establishing process of establishing the multimediasession, refer to the step a1 in the proceeding embodiment.

Step c2: The UE3 sends to the application server a media stream addingrequest to add the media stream between the UE3 and the UE2, where therequest includes the added media type of the media stream.

In the embodiment of the present invention, the media stream addingrequest includes the identity of the UE1 to indicate to the applicationserver which UE needs to be added with the media stream in the session.

It is understandable that the identity of the UE3 may help theapplication server to identify which UE needs to be added with the mediastream.

The identity of the UE3 is its global routable address; if the UE1 andthe UE2 are user terminals registered in an IM Public user identity,IMPU, the UE1 that associates with the UE3 may be searched out accordingto the IMPU of the UE3.

The present IP multimedia subsystem, IMS, supports multiple UEs toregister in an IP IMPU, ie, one-user-multiple-terminals. In theapplication, the IMS is required to differentiate the informationsources and send the information to one specified UE that registers inthe IMPU and this is feasible with the Globally Routable User Agent (UA)URIs, GRUU. For example,

When the UE registers with the IMS, the UE sends out the GRUU allocationrequest, and the allocation request includes:sip:bob@3gpp.org.gruu;opaque=“urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6”,where the “bob@3gpp.org;gruu” is user's IMPU; “opaque” identifies one UEof multiple UEs; “S-CSCF” is to return “bob@3gpp.org;gr=kjh29×97us97d”,where “gr” parameter is selected by CSCF to identify the UE.

As can be seen from the above, under the situation of one user twoterminals, the UEs of the user are registered with the same IMPU; while,in the process of IMS registration, GRUU is allocated to identifyindividual UEs. In the embodiments of the present invention, the UE3 andthe UE2 sharing the IMPU also fall into the situation ofone-user-multiple-terminals; therefore, after the application serverreceives the media stream adding request, it may search out the UE1 bythe IMPU of the UE3.

It is understandable that the media stream adding request may alsoinclude the multimedia session identity, which identifies the session tobe added with the media stream. In the IMS, the UE may be participatingin more than one session at the same time, and through the abovementioned method, it is identifiable in which session of the UE themedia stream is to be added.

Step c3: The UE3 establishes the media stream of the media type with theUE2 under the control of the application server. The process ofestablishing the media stream of the media type may refer to step a3 ofthe first embodiment.

It is understandable that before step c3, the following may be included.The application server asks the UE1 for instructions whether to allowthe UE3 to add the media stream of the media type; if yes, the UE1confirms with the application server, and proceeds with step c3.

The difference between the second embodiment and the first embodimentlies in that the UE3 initiates the media stream adding request, which isapplicable for more scenarios; therefore, more approaches are providedfor the media stream transfer to facilitate the using of the user.

It is understandable to those of ordinary skill in the art that thewhole or part of the steps in the above embodiments may be accomplishedby a program ordering the related hardware. The program may be stored ina computer readable storage medium and may include the following stepswhen being executed:

The UE1 establishes a multimedia session with the UE2 under the controlof the application server.

The UE sends to the application server a media stream adding requestdirected at a multimedia session; the media stream adding requestincludes the identity of the UE3 and the media type of the media streamrequested to be added.

The UE3 establishes with the UE2 the media stream of the media typeunder the control of the application server.

The above mentioned storage medium may be a read-only memory, disk orcompact disk.

The following is an example of implementing the method in the firstembodiment by adopting the SIP. In this example, supposing user Bob ownstwo terminals: the UE1 and the UE3, where both of the two UEs registerwith the IMS in a same public user identity “Bob@sipo.com”, and the GRUUare respectively Bob@sipo.com;gr=erwiopuel andBob@sipo.com;gr=dfweyuiue3. The gr values are erwiopuel and dfweyuiue3to differentiate the the UE1 and the UE3.

The signaling flow is as shown in FIG. 4, including the following steps:

Step d1: The UE2 sends an Invite message to S-CSCF to invite the UE1 tojoin in the multimedia session, where the Invite message includesBob@sipo.com;gr=erwiopuel, Call-ID: 3456df0u, and the Call-ID is thecalling identity to identify the current calling; and the Invite messagefurther includes the media type that is requested to be established,which, in this embodiment, are audio, video, and real-time textmessages.

Step d2: The S-CSCF performs the called iFC check on the UE1 andacquires that the UE1 supports the media stream transfer service, andthen sends the Invite message to the application server, where the sentInvite message includes an added address of the S-CSCF and a dialogidentifier parameter (dia-id); the added S-CSCF address is to facilitatethe returning of the request to the S-CSCF by the application serverwhen the process completes; the added dia-id is for the S-CSCF todifferentiate the succeeding requests from the currently receivedrequest.

Step d3: The application server generates a new Invite message and sendsthe message to the UE1, where the Invite message includes the S-CSCFaddress and the dia-id; the Invite message is firstly sent to theS-CSCF, and then the S-CSCF identifies the calling request through thedia-id in the message and continues the iFC check; when the check iscompleted, the application server sends a calling request to the UE1.

Step d4: The UE1 sends a response message (200 OK) to the UE2, and thenthe UE1 establishes a call with the UE2 to start the multimedia callamong media stream 1, media stream 2 and media stream 3.

Step d5: Under the control of the user Bob, the UE1 sends the mediastream adding request to the application server; the media stream addingrequest is realized through the Subscribe message of the SIP; theSubscribe message includes the media stream type (m=4) wished to beadded, ie media stream 4, and the identity of the UE3 of which the mediastream is to be added, ie GRUU:Bob@sipo.com;gr=dfweyuiue3.

Step d6: The application server sends to the UE1 the media addingconfirmation by adopting the Notify message of the SIP to answer theUE1.

It is understandable that since a calling has been established betweenthe application server and the UE1, the sent media transfer request maybe in the form of re-Invite or Update, and the corresponding response tobe returned may adopt the 200 OK.

Step d7: The application server generates another new Invite message(Call-ID: 2876oj68, Route: scscf1; dia-id=8736yuhs) to send to the UE3;the Invite message is firstly sent to the S-CSCF, and the S-CSCFidentifies the calling request through the dia-id, and send the callingrequest to the UE3; the application server may also send the mediainformation about the media stream 4 of the UE3 through the callingrequest, and the information may include an IP address, a port, a codingformat, etc.

In the process of establishing the multimedia session of steps d1-d4, ifthe session initiator is the UE1, the application server sets theaddress of the application server as the calling address in the Invitemessage and sends the calling request to the UE3. It is not supported bythe present network that the application server sets the identity of theUE2 as the calling address; if, however, the application server sets theidentity of the UE2 as the calling address, it is considered that theapplication server initiates a calling request to the UE3 in place ofthe UE1, which may cause logic processing confusion at the applicationserver and increase the processing complexity at the network side.

Step d8: The UE3 makes a 200 OK response.

Step d9: After receiving the 200 OK, the application server generatesre-Invite or Update message, and through the message, the mediainformation of the UE3 is sent to the UE2, so that the UE3 establishesmedia stream 2 with the UE2.

The re-Invite or Update message is used for the session re-negotiation,such as adding or deleting a media stream, or modifying the IP addressof the media stream. It is understandable that the negotiation processmay be repeated, but the specific times do not limit the presentinvention.

Step d10: The UE2 returns the acknowledgement message (200 OK) to acceptthe session negotiation request, where the acknowledgement messageincludes media information of the UE2.

Now, the user Bob establishes a multimedia call with the user Tom of theUE2 through the UE1 and UE3.

Step d11: The applications sever sends the media information of the UE2through the ACK message to the UE3.

Now, the user Bob establishes a multimedia calling with the user Tom ofthe UE2 through the UE1 and UE3.

In FIG. 4, the dotted line represents the media stream transmittingstate before and after the media stream transfer.

The following is an example of implementing the method in a secondembodiment by adopting the SIP. In this example, supposing user Bob ownstwo terminals: the UE1 and the UE3, where both of the two UEs registerwith the IMS in a same public user identity “Bob@sipo.com”, and the GRUUis respectively Bob@sipo.com;gr=erwiopuel andBob@sipo.com;gr=dfweyuiue3. The gr values are erwiopuel and dfweyuiue3to differentiate the UE1 and the UE3.

The signaling flow is as shown in FIG. 5, including the following steps:

Step e1: The UE2 sends an Invite message to S-CSCF to invite the UE1 tojoin the multimedia session, where the Invite message includesBob@sipo.com;gr=erwiopuel, Call-ID: 3456df0u, and the Call-ID is thecalling identity to identify the current calling; and the Invite messagefurther includes the media type that is requested to be established,which, in this embodiment, are audio, video, and real-time textmessages.

Step e2: The S-CSCF performs the called iFC check on the UE1 andacquires that the UE1 supports the media stream transfer service, andthen sends the Invite message to the application server, where the sentInvite message includes an added address of the S-CSCF and a dialogidentifier parameter (dia-id); the added S-CSCF address is to facilitatethe returning of the request to the S-CSCF by the application serverwhen the process completes; the added dia-id is for the S-CSCF todifferentiate the succeeding requests from the currently receivedrequest.

Step e3: The application server generates a new Invite message and sendsthe message to the UE1, where the Invite message includes the S-CSCFaddress and the dia-id; the Invite message is firstly sent to theS-CSCF, and then the S-CSCF identifies the calling request through thedia-id in the message and continues the iFC check; when the check iscompleted, the application server sends a calling request to the UE1.

Step e4: The UE1 sends a response message (200 OK) to the UE2, and theUE1 establishes a call with the UE2 to start the multimedia call amongmedia stream 1, media stream 2 and media stream 3.

Step e5: The user Bob controls the UE3 to send a switching request ofthe media stream 2 to the application server, where the switchingrequest is identified by the VDI/VDN; the application server searchesout the session of the media to be transferred through the identity ofthe UE3 (Bob@sipo.com;gr=dfweyuiue3).

Step e6: The application server informs the UE1 through the INFO messagethat the UE3 requests the adding of the media stream 4.

Step e7: If receiving the media stream switching request, the UE1responds to the request through INFO information.

Step e8: The application server generates re-Invite or Update message,and through the message, the media information of the UE3 is sent to theUE2.

Step e9: The UE2 receives the media information of the UE3 and returnsthe 200 OK to confirm.

Step e10: The application server sends the 200 OK to the UE3, and sendsthe media information of the UE2 to the UE3, so that the UE3 establishesthe media stream 4 with the UE2.

The re-Invite or Update message is used for the session re-negotiation,such as adding or deleting media stream, or modifying the IP address ofthe media stream. It is understandable that the negotiation process maybe repeated, but the specific times do not limit the present invention.

Now, the user Bob establishes a multimedia calling with the user Tom ofthe UE2 through the UE1 and UE3.

A third embodiment of the present invention provides a UE, including:

a session establishing unit, adapted to establish a session with the UE2under the control of the application server;a media adding request sending unit, adapted to send a media addingrequested directed at the multimedia session to the application server,where the media adding request includes the identity of the UE3 and themedia type of the media stream requested to be added.

A fourth embodiment of the present invention provides an applicationserver, including:

a session control unit, adapted to control the UE1 to establish amultimedia session with the UE2;a receiving unit, adapted to receive a media stream adding request ofthe UE1 which is directed at the multimedia session; where the mediastream adding request includes the identity of the UE3 and media type ofthe media stream requested to be added; anda media adding control unit, adapted to control the UE3 to establish themedia stream of the media type with the UE2.

A fifth embodiment of the present invention provides a user equipment,including:

a media adding request sending unit, adapted to send the request foradding the media stream between the application server and the UE2;where the request includes the type of the added media stream;a media stream establishing unit, adapted to establish the media streamof the added media type with the UE2 under the control of theapplication server;

A sixth embodiment of the present invention provides an applicationserver, including:

a session control unit, adapted to control the UE1 to establish amultimedia session with the UE2;a receiving unit, adapted to receive the media stream adding requestsent by the UE3 to add the media stream between the UE3 and the UE2,where the request includes the media type of the added media stream;a media stream adding unit, adapted to control the media stream of themedia type established between the UE3 and the UE2.

The above is the detailed description of the method, UE and applicationserver for adding media stream. In one embodiment of the presentinvention, the multimedia session is established between the UE1 and theUE2 under the control of the application sever; the UE1 sends to theapplication server a media stream adding request directed at themultimedia session, where the media stream adding request includes theUE3 identity and the media type of the media stream requested to beadded; the UE3 establishes the media stream of the media type with theUE2 under the control of the application server. Therefore, adding themedia stream on the UE3 is realized, and the user may realize themultimedia session with the peer end through multiple UEs, therebyavoiding the inconvenience that the media stream can only be added tothe two parties in the session and living up to the users' diversifiedrequirements on the multimedia services.

Another embodiment differs from the above in that the UE3 initiates themedia stream adding request, which is applicable for more scenarios;therefore, more approaches are provided for the media stream transfer tofacilitate the using of the user.

It is apparent that those skilled in the art can make modifications andvariations to the invention without departing from the spirit and scopeof the invention. To summarize, the specification above is not intendedto limit the protection scope of the present invention.

1. A method for adding a media stream for a multimedia session,comprising, controlling a first user equipment, UE1, to establish amultimedia session with a second user equipment, UE2; receiving a mediastream adding request directed at the multimedia session of the UE1,where the media stream adding request comprises: an identity of a UE3 ora media type of the media stream requested to be added; and controllingthe UE3 to establish a media stream of the media type with the UE2. 2.The method of claim 1, wherein the controlling the UE3 to establish amedia stream of the media type with the UE2 comprises, sending to theUE3 the session Invite; controlling the UE3 and the UE2 to perform themedia information negotiation directed at the media type; andtransmitting, by the UE3, the media stream of the media type to the UE2when the negotiation succeeds.
 3. The method of claim 2, wherein, in thesession Invite sent to the UE3, the address of the calling party is anaddress of an application server or an identity of the UE2.
 4. Themethod of claim 1, wherein, before receiving a media stream addingrequest directed at the multimedia session of the UE1, the UE1 receivesthe media stream adding request sent by the UE2, where the media streamadding request comprises the media type of the added media stream.
 5. Amethod for adding a media stream for a multimedia session, comprising,controlling a first user equipment, UE1, to establish a multimediasession with a second user equipment, UE2; receiving a media streamadding request sent by a third user equipment, UE3, to establish a mediastream with the UE2, where the media stream adding request includes amedia type of the added media stream; controlling the UE3 to establishthe media stream of the media type with the UE2.
 6. The method of claim5, wherein, before controlling the UE3 to establish the media stream ofthe media type with the UE2, the UE1 asks for instructions whether toallow the UE3 to add the media stream of the media type; if yes, the UE1returns the confirmation, and the UE3 is furthered controlled toestablish the media stream of the media type with the UE2.
 7. The methodof claim 5, wherein the media stream adding request comprises anidentity of the UE1.
 8. The method of claim 7, wherein the media streamadding request further comprises a multimedia session identity.
 9. Themethod of claim 5, wherein, after receiving a media stream addingrequest sent by a UE3 to establish a media stream with the UE2, the UE1that associates with the UE3 is searched out according to the identityof the UE3.
 10. A user equipment (UE), comprising: a sessionestablishing unit, adapted to establish a session with a second userequipment, UE2, under the control of an application server; a mediaadding request sending unit, adapted to send a media stream addingrequest directed at the multimedia session to the application server,wherein the media adding request comprises an identity of a third userequipment, UE3, and a media type of the media stream requested to beadded.
 11. An application server, comprising: a session control unit,adapted to control a first user equipment, UE1, to establish amultimedia session with a second user equipment, UE2; a receiving unit,adapted to receive a media stream adding request of the UE1 which isdirected at the multimedia session, wherein the media stream addingrequest comprises an identity of a third user equipment, UE3, and amedia type of the media stream requested to be added; and a media addingcontrol unit, adapted to control the UE3 to establish media stream ofthe media type with the UE2.
 12. A user equipment, UE, comprising: amedia adding request sending unit, adapted to send a request for addinga media stream between an application server and a second userequipment, UE2, wherein the request comprises a type of the added mediastream; and a media stream establishing unit, adapted to establish themedia stream of the added media type with the UE2 under the control ofthe application server.
 13. An application server, comprising: a sessioncontrol unit, adapted to control a first user equipment, UE1, toestablish a multimedia session with a second user equipment, UE2; areceiving unit, adapted to receive a media stream adding request sent bya third user equipment, UE3, to add a media stream between the UE3 andthe UE2, where the request comprises the media type of the added mediastream; and a media stream adding unit, adapted to control the UE3 toestablish media stream of the media type with the UE2.